Magnetoresistive sensor with magnetostatic coupling of magnetic regions

ABSTRACT

A magnetic field sensor is described incorporating a plurality of magnetic stripes spaced apart on the surface of a substrate such that the stray magnetic fields at the ends of the magnetic stripes are magnetostatically coupled and the magnetic stripes are magnetized respectively in alternating directions, nonmagnetic conductive material positioned in the spaces between the magnetic stripes and electrodes for passing current crosswise through the plurality of magnetic stripes to detect a change in resistance by the giant magnetoresistive effect (MGR). The invention overcomes the problem of detecting low magnetic fields since the magnetic fields required to saturate magnetic stripes depends on the magnetostatic coupling which in turn can be controlled by the geometry and position of the magnetic stripes in the sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of application Ser. No.08/414,865, filed Mar. 31, 1995 now U.S. Pat. No. 6,510,031.

FIELD OF THE INVENTION

This invention relates to magnetoresistive sensors and more particularlyto giant magnetoresistive effect (GMR) sensors using controlledmagnetostatic coupling to obtain opposite alignment of magnetic regionsof soft magnetic materials.

BACKGROUND OF THE INVENTION

The giant magnetoresistive effect (GMR) depends on having magneticregions which are not aligned with respect to each other in a zeroamplitude magnetic field. When the magnetic regions are at saturation ina magnetic field, the magnetization in the magnetic regions are fullyaligned. The GMR of magnetic regions in magnetic saturation is definedas the change in resistance from zero magnetic field to the resistanceat magnetic saturation normalized by the zero field resistance.

Giant magnetoresistance has been discovered in magnetic multilayers. Ina publication by S. S. P. Parkin et al., Phys. Rev. Lett. 64, 2304(1990), the magnetoresistance in metallic superlattice structures ofCo/Ru, Co/Cr, and Fe/Cr was reported. Values of ΔR/R of up to 33 percenthave been observed in a Fe/Cr superlattice structure. This can becompared to ΔR/R of a few percent for the anisotropic magnetoresistanceof a simple permalloy thin film sensor.

In a publication by W. P. Pratt et al., Phys. Rev. Lett. 66, 3060(1991), in magnetic multilayers of Ag/Co, the magnetoresistance with thecurrent flow perpendicular to the layer has the largest change ofresistance, for example, near 50 percent as compared to themagnetoresistance of current in the plane of the layer which may have aΔR/R of 12 percent. Also, in multilayer structures, the magnetic fieldsrequired to obtain the large values of ΔR/R are very large because themagnetic field must be sufficient to overcome the antiferromagneticexchange between the layers. These magnetic fields are much larger thanthe fringing field of a magnetic transition on a disk or taperepresenting stored data.

In exchange coupled films, the magnetic field required to align theoppositely magnetized regions depends on the strength of theantiferromagnetic exchange between the layers. The magnetic fieldrequired to align the oppositely magnetized regions tend to be verylarge, for example, on the order of 10 kOe.

A spin valve is a sandwich structure of two magnetic layers with anonmagnetic layer between such as described in U.S. Pat. No. 5,159,513which issued on Oct. 27, 1992 to B. Dieny et al. In a spin valve, onemagnetic layer has its magnetic orientation fixed, usually by exchangedcoupling. The other magnetic layer is free to switch in the appliedfield except for its own coercivity (Hc) hysteresis. The resistance ofthe device is highest when the magnetic fields are oppositely aligned oraligned perpendicularly and the lowest resistance is when the magneticfields are aligned. The magnitude of the giant magnetoresistive effectin spin valve structures may be seven to nine percent as shown in U.S.Pat. No. 5,159,513 which is not as high as in multilayer structures.

The giant magnetoresistive effect has also been reported in granularthin films in a publication by J. Q. Xiao et al., Phys. Rev. Lett. 68,3749 (1992). These granular thin films consist of small phase separatedsingle domain magnetic particles, for example, Co in Cu, a nonmagneticconductive matrix. So far, the giant magnetoresistive effect has onlybeen observed in a limited set of materials which phase separate intosuitable magnetic and nonmagnetic regions. The magnetization is orientedalong the easy axis of each particle which varies randomly from particleto particle. The magnetic field must overcome the magnetocrystallineanisotropy and the shape anisotropy of the Co particles. In addition, ifthere is any interfacial strain at the Cu/Co interface, there may be anadditional anisotropy through the magnetostriction (λ). The magneticfield necessary to overcome the random directions by local anisotropy ison the order of 10 kOe. Also, ΔR/R is smaller than in multilayerstructures, probably because the change in alignment is less extreme,being from random to parallel rather than from perpendicular to parallelor antiparallel to parallel.

SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus for sensing amagnetic field by the giant magnetoresistive effect (GMR) is describedcomprising a plurality of magnetic stripes spaced apart on the uppersurface of a substrate such that the stray fields at the ends of themagnetic stripes provide a magnetostatic coupling which magnetizes themagnetic stripes in alternating directions in a zero magnetic field, anonmagnetic conductive material such as copper, positioned in the spacesbetween the magnetic stripes to form a conductive path betweenrespective stripes, and terminals or electrodes for introducing currentalong the conductive path for detecting the change in resistance throughthe plurality of stripes and conductive paths as a function of magneticfields applied to the magnetic stripes. The magnetic stripes may berectangular in shape and spaced apart from one another by at least 100 Åto prevent any exchange coupling. The magnetic stripes may comprise asoft magnetic material. The magnetostatic coupling between ends ofmagnetic stripes may be enhanced by positioning transverse magneticstripes over or abutted to the ends which function as permeable“keepers”. The cross-sectional areas of the magnetic stripes may be lessthan 1000 Å square. The apparatus is suitable for incorporation in ahead for sensing a magnetic disk in a magnetic disk operating system.When the magnetic stripes are magnetized in alternating directions, ahigh resistance state is measured to current passing through theplurality of magnetic stripes and when a magnetic field causes themagnetic stripes adjacent one another to be magnetized in the samedirection, a low resistance state is measured to current passing throughthe plurality of magnetic stripes.

The invention further provides, a method for fabricating a magnetic headcomprising the steps of orienting, cutting and polishing or selecting asingle crystal substrate having a surface at an angle between 1 and 10°away from a major crystallographic plane, annealing the crystal toproduce atomic scale steps on its surface, depositing a ferromagneticmetal such as Fe, Co, or Ni or alloys thereof onto the single crystalsubstrate surface, overcoating the ferromagnetic metal with anonmagnetic metal of comparable thickness and planarizing thenonmagnetic metal to form alternating regions of magnetic andnonmagnetic metals on the surface of the substrate.

The invention provides a plurality of magnetic stripes of soft magneticmaterial spaced apart for controlled magnetostatic coupling therebetweento obtain opposite alignment of the magnetization of adjacent stripes inzero magnetic field.

The invention further provides an apparatus for sensing a magnetic fieldwherein the magnetic field required for magnetic saturation depends onthe magnetostatic coupling which can be controlled by way of thegeometry of the magnetic stripes and their spacing.

The invention further provides an apparatus for sensing a magnetic fieldwherein the magnetic stripes are made of soft magnetic materials such asiron, nickel or alloys thereof having high permeability, low coerciveforce and small hysteresis loss so that the anisotropy magnetic fieldsare small and do not dominate the magnetic saturation field as ingranular films. The distance between the magnetic regions or betweenmagnetic stripes is large enough such as 100 Å such that the magneticstripes are not strongly exchanged coupled to the adjacent magneticstripe respectively.

BRIEF DESCRIPTION OF THE DRAWING

These and other features, objects, and advantages of the presentinvention will become apparent upon consideration of the followingdetailed description of the invention when read in conjunction with thedrawing in which:

FIG. 1 is a first perspective view of a first embodiment of theinvention.

FIG. 2 is a second perspective view diagram of the first embodiment ofthe invention.

FIG. 3 is a perspective view of a second embodiment of the invention.

FIG. 4 is a first top view of FIG. 3.

FIG. 5 is a second top view of FIG. 3.

FIG. 6 is a top view of a third embodiment of the invention.

FIG. 7 is a top view of a fourth embodiment of the invention.

and FIG. 8 is a perspective view of a fifth embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, a magnetic head 10 for sensing a magneticfield is shown. A plurality of magnetic stripes 12 through 15, arespaced apart such as by nonmagnetic conducting stripes 16 through 19.Magnetic stripes 12 through 15 and nonmagnetic stripes 16 through 19 arepositioned adjacent one another, side by side, in electrical contact toone another on substrate 22. Substrate 22 may be nonmagnetic andnonmetallic such as ceramic, glass, sapphire, quartz, magnesium oxide,semi-insulating such as silicon, silicon germanium, gallium arsenide,silicon-on-insulator or a polymer. Substrate 22 has a lower surface 23upon which magnetic stripes 12 through 15 and nonmagnetic conductivestripes 16 through 19 are positioned. Magnetic stripe 12 is electricallycoupled to electrode 26 which may, for example, extend along surface 23and wrap around the end of substrate 22. Nonmagnetic conductive stripe19 is coupled to electrode 28 which may for example extend along surface23 and wrap around the end of substrate 22 at the end opposite electrode26. Substrate 22 and electrode 26 may be supported by arm 29. Electrode28 and substrate 22 may be supported by arm 30. Arms 29 and 30 functionto position magnetic head 10 with respect to magnetic media 32 having anupper surface 33 as shown in FIG. 1 such as transverse or 90° tomagnetic media 32 as shown in FIG. 2. Magnetic media 32 may be forexample a magnetic disk having a layer of magnetic material thereonsuitable for storing information. Arms 29 and 30 may be rigid and in afixed relationship to one another.

Magnetic stripes 12 through 15 may be made of soft magnetic materialsuch as iron, nickel or alloys thereof having high permeability, lowcoercive force and small hysteresis loss so that anisotropy fields aresmall and do not dominate the saturation field of the respectivemagnetic stripe. The ends of magnetic stripes 12 through 15 arepositioned with respect to one another to foster magnetic couplingbetween respective ends of magnetic stripes resulting in odd or evenmagnetic stripes 12 through 15 being magnetized in opposite directionsto respective even or odd magnetic stripes as shown in FIG. 2. Forexample, magnetic stripes 12 and 14 are magnetized in a first directionshown by arrows 36 and 37 which are parallel and correspond thelongitudinal axes 38 and 39 respectively. Magnetic stripes 13 and 15 aremagnetized in a second direction opposite to the first direction shownby arrows 42 and 43 which are parallel to the longitudinal axes 44 and45 respectively.

The magnetostatic coupling from a first end of magnetic stripe 13 isshown by arrows 48 and 49. Arrow 48 represents the magnetostaticcoupling to a first end of magnetic stripe 12 and arrow 49 representsthe magnetostatic coupling to a first end of magnetic stripe 14. Arrow50 represents the magnetostatic coupling from a second end of magneticstripe 12 to a second end of magnetic stripe 13. Arrow 51 represent themagnetostatic coupling from a second end of magnetic stripe 14 to asecond end of magnetic stripe 13. Arrow 52 represents the magnetostaticcoupling from a second end of magnetic stripe 14 to a second end ofmagnetic stripe 15. Arrow 53 represents the magnetostatic coupling froma first end of magnetic stripe 15 to a first end of magnetic stripe 14.Each magnetic stripe may have about equal magnetostatic coupling such asshown by arrows 48 and 49 to the adjacent magnetic stripes 12 and 14.The number of magnetic stripes may be in the range from 2 to about10,000. The magnetic stripes 12 through 15 are separated from oneanother by a distance such as 100 Å which is large enough so that theyare not strongly antiferromagnetic exchanged coupled. The externalmagnetic field with the magnetostatic coupling as shown in FIG. 2corresponds to an applied magnetic field H of zero shown by arrow 55.With opposite magnetic alignment of adjacent magnetic stripes 12 through15, magnetic head 10 is in a high electrical resistant state betweenelectrodes 26 and 28.

FIG. 1 shows the low electrical resistant state of magnetic head 10where magnetic stripes 12 through 15 are magnetized in the samedirection as shown by arrows 57 in the presence of an applied magneticfield H shown by dashed arrows 58. The low and high electricalresistance state of magnetic head 10 may be detected by passing anelectrical current through the plurality of magnetic stripes andplurality of nonmagnetic conductors by way of electrodes 26 and 28.Current source 60 provides current over leads 61, through resistor 62and over lead 63 to electrode 28. Current from electrode 26 is coupledover lead 64 back to current source 60. The voltage across leads 63 and64 provide an indication of the resistance of magnetic head 10.

Referring to FIG. 1, in operation magnetic media 32 may have informationstored therein in track 67 in the form of magnetic domains 68 through73, with magnetic domain walls 74, 76, and 79-81 there between. Asmagnetic media is moved as shown by arrow 75, magnetic domains 68through 73 pass underneath magnetic head 10 and in close proximity tomagnetic stripes 12 through 15. As magnetic domain 71 passes undermagnetic head 10, fringe magnetic fields shown by arrows 58 are alignedin the same longitunal direction as magnetic stripes 12 through 15 andmagnetically saturate magnetic stripes 12 through 15 in the longitudinaldirection as shown by arrows 57. The resistance of the current passingthrough magnetic stripes 12 through 15 from electrode 28 to electrode 26or vice-versa will be low due to the giant magnetoresistive effect(GMR). As magnetic domain 72 passes underneath magnetic head 10, thefringe magnetic field shown by arrows 77 will cause magnetic stripes 12through 15 to magnetically saturate in the opposite direction. Asmagnetic stripes 12 through 15 change direction in magnetization, themagnetoresistance state will be high due to the misalignment of themagnetization due to the partial change of magnetic direction experienceas magnetic domain 72 moves underneath magnetic head 10. When magneticdomain 72 is completely underneath magnetic head 10, fringe magneticfields shown by arrows 77 are aligned with the longitudinal direction ofmagnetic stripes 12 through 15 and magnetically saturate magneticstripes 12 through 15 in the longitudinal direction opposite to thatshown by arrows 57. The electrical resistance through magnetic head 10via electrodes 26 and 28 will be low due to the giant magnetoresistiveeffect (GMR). Arrows 78 show the direction of fringe magnetic fields formagnetic domain 73 which may be in the same direction as magnetic domain72. When magnetic head 10 moves from being over magnetic domain 72 tobeing over magnetic domain 73, the electrical resistance throughmagnetic head 10 via electrodes 26 and 28 will remain low as magneticstripes 12 through 15 will remain magnetically saturated in the samedirection as when magnetic head was over magnetic domain 72.

The magnetic field to be sensed such as shown by arrows 58 in FIG. 1,may be applied in the plane of the device i.e., parallel to surface 23of which magnetic stripes 12 through 15 are positioned and throughmagnetic stripes 12 through 15. The electrical resistance betweenelectrodes 26 and 28 will decrease until magnetic stripes 12 through 15are saturated in the direction of the applied magnetic field which maybe 30 Oe or less as shown by arrows 58 with respect to magnetic domain70 which is the low GMR state.

Referring to FIG. 2, magnetic head 10 is positioned so that the magneticstripes 12-15 are aligned transverse to surface 33 of magnetic media 32to intercept transverse fringe magnetic fields shown in FIG. 1 frommagnetic domains 71 and 72 at or near domain wall 79. Magnetic media 32and more particularly track 67 is moving underneath magnetic head 10.The vertical or transverse (vertical) component of the magnetic domainshown by arrows 58 and 77 in FIG. 1 cause magnetic stripes 12-15 to bemagnetically aligned in parallel lowering the resistance of magnetichead 10. For example, when the magnetic stripes 12-15 are approachingdomain wall 79 but are still in the region of magnetic domain 71 wherethe fringe fields, shown by arrows 58 in FIG. 1, are parallel to surface33, the magnetic stripes will be alternately magnetized due tomagnetostatic coupling from adjacent magnetic stripes. When the fringemagnetic fields become vertical or transverse upon approaching the endof magnetic domain 71 near domain wall 79 as shown by arrows 58 in FIG.1, the magnetization of magnetic stripes 12-15 will be directed in thedown direction as shown by arrow 36. Magnetic head 10 will be in the lowresistance state with the magnetization of magnetic stripes 12-15aligned parallel.

As media 32 moves domain wall 79 past magnetic stripes 12-15, themagnetic stripes will be magnetized in the down direction near domainwall 79. As media 32 moves domain wall 79 way past magnetic stripes12-15, the fringing magnetic fields of domain 72 will be parallel tosurface 33 and there will be no vertical or transverse magneticcomponent to magnetize magnetic stripes 12-15. Magnetic head 10 will bein the high resistance state.

FIG. 3 shows an alternate embodiment of the invention where in additionto the plurality of magnetic stripes 12 through 15 and nonmagneticconducting stripes 16 through 19 on substrate 22′, there are magnetickeepers 82 and 83 positioned over the ends of the magnetic stripes 12through 15 as shown in FIG. 3. In FIG. 3 like references are used forfunctions corresponding to the apparatus of FIGS. 1 and 2. Keepers 82and 83 function to strengthen or reinforce the magnetostatic couplingconnecting the ends of the stripes 12 through 15.

For optimal performance, a nonmagnetic electrically insulating spacer 84must separate magnetoresistive stripes 12-15, together with theintervening nonmagnetic conductors 16-19, from the two keepers 82 and83. Spacer 84 serves to (1) prevent exchange stiffness coupling whichwould tend to align the stripe magnetizations in the same direction,thus counteracting the beneficial keeper effect, and (2) prevent thekeepers, if conducting, from short circuiting magnetoresistive stripes12-15. Spacer 84 thickness may be in the range from about 50 Å to about200 Å and is optimally about 100 Å in thickness and needs no lithographysince it can blanket over magnetic stripes 12-15 and nonmagneticconductive stripes 16-19.

FIG. 4 is a first top view of FIG. 3 showing the magnetic fields andmagnetic stripes 12 through 15, non magnetic stripes 16-19 and keepers82 and 83. The magnetic flux carried by each magnetic stripe 12 through15 respectively is divided in two parts at its ends, each part closingthrough one of the neighboring magnetic stripes. Therefore, thesaturation or magnetic flux capacity of each keeper 82 and 83 should beone half of the saturated magnetic flux capacity of stripes 12 through15 respectively. In FIG. 4, flux paths 86 and 87 are shown passingthrough magnetic stripe 13 with flux path 86 passing through magneticstripe 12 and flux path 87 passing through magnetic stripe 14. Fluxpaths 87 and 88 pass through magnetic stripe 14 in the oppositedirection of flux paths 87 and 86 passing through magnetic stripe 13.Flux path 88 passes through magnetic stripe 15.

Magnetic stripe 15 has flux paths 88 and 89 passing through it inopposite directions as flux paths 88 and 87 in magnetic stripe 14. Fluxpath 89 also passes through magnetic stripe 20.

Referring to FIG. 5, a magnetic field may be applied perpendicular tothe longitudinal axis of the magnetic stripe such as perpendicular toaxes 38 and 44 of magnetic stripes 12 and 13 shown on FIG. 5. An appliedmagnetic field H shown by arrow 95 perpendicular to the longitudinalaxis will produce parallel alignment of the magnetization withinmagnetic stripes 12 and 13 when the demagnetization field of themagnetic stripe is overcome. The demagnetizing field B is shown inequation 1.

4πM=4πM ₈ h/(w+h)  (1)

In equation 1, h as shown in FIG. 5 by arrow 93 is equal to the heightof the magnetic stripe and W as shown in FIG. 5 by arrow 94 is equal tothe width of the magnetic stripe. The term M₈ is the saturationmagnetization. One advantage of applying a magnetic field Hperpendicular to the longitudinal axis of the magnetic stripe is thatthe magnetic transition within the material is by rotation and thereforefaster, more nearly linear, and free of hysteresis. The magnetic field Bin a magnetic stripe such as magnetic stripe 12 shown on FIG. 5 is givenin equation 2 where

H shown by arrow 95 is the applied field and 4πM is a demagnetizationfield.

B=H+4πM  (2)

As shown in FIG. 5, for sufficiently small magnetic stripes with crosssections, less than 1000 square angstroms, domain walls will nucleatethermally. Then the magnetic response will not have a threshold, andhysteresis will be absent. In this regime, the permeable keepers 82 and83 shown in FIG. 4 will have less influence on the behavior of themagnetic stripes. Statistical correlation between positions of mutuallyattractive north (N) and south (S) magnetic domain walls will tend topreserve antiparallelism of neighboring magnetic stripe regions by wayof magnetic flux paths in and between magnetic stripes 12 and 13 shownin FIG. 5 by arrows 96 through 101. Also, the magnetostatic couplingbetween magnetic stripes depends on the spacing between the magneticstripes. The magnetic stripes will however be spaced to prevent exchangecoupling.

Referring to FIG. 6, a magnetic array 110 of magnetic stripes 103through 108 is shown spaced apart on surface 23 of substrate 22 whichare generally parallel to one another. Magnetic stripes 103 through 108may be spaced apart by a first distance shown by arrow 109. Magneticstripes 111 through 114 are shown spaced apart, generally parallel toone another and transverse to and over lapping magnetic stripes 103 to108. Magnetic stripes 111 through 114 may have a spacing from oneanother shown by arrow 115. Non magnetic stripes 181 through 185 fillthe space between magnetic stripes 103 and 108 to provide an electricalcurrent path through magnetic stripes 103 through 108. Crossed or overlapping magnetic stripes 111 through 114 function as permeable keepersas permeable keepers 82 and 83 in FIG. 4.

For optimal performance, a nonmagnetic electrically insulating spacer116 must separate magnetoresistive stripes 103-108, together with theintervening non-magnetic stripes 181-185, from magnetic stripes 111-114which function the same as keepers 82 and 83 in FIG. 3.

The magnetic stripes 103 through 108 have segments between intersectionsor cross stripes 111 through 114 to provide independent flux paths someas shown in FIG. 4. For example magnetic stripe segment 118 of magneticstripe 104 has a flux path similar as shown for magnetic stripe 13 inFIG. 4. The magnetic flux shown by arrow 119 divides at cross magneticstripe 111 with about one half of the magnetic flux going down shown byarrow 120 and one half of the magnetic flux going up shown by arrow 121.The path of flux 120 follows magnetic stripe 105 and crossed magneticstripe 112 shown by arrows 122 and 123. The path of flux 121 is overmagnetic stripe 103 and crossed magnetic stripe 112 shown by arrows 124and 125. The flux paths are formed by the magnetostatic coupling betweencross magnetic stripes 111 and 112 to magnetic stripes 103 and 104 wherethey cross over. A magnetic field H may be applied in the plane ofmagnetic stripes 103 through 108 as shown by arrow 128 which will causethe magnetic field within magnetic stripes 103 through 108 to be alignedparallel and thus have lower resistance with respect to current passingthrough the array.

In one electrical arrangement for detecting the change in resistanceacross magnetic array 110 would be to have cross magnetic stripes 111through 114 insulated from magnetic stripe 103 to 108 and to haveconductive nonmagnetic material 181 through 185 between stripes 103through 108 as shown in FIG. 6. The outside current could be applied byway of leads 131 and 132 across magnetic array 110. When themagnetization in magnetic stripe 103 through 108 are aligned parallel,the magnetic array 110 will be in its low resistance state. When themagnetization is oppositely aligned from stripe segment to stripesegment as shown in FIG. 6 by the arrows 119, 122 and 124, magneticarray 110 will be in the high resistance state.

FIG. 7 shows a top view of magnetic device 136 for sensing a magneticfield. Device 136 consists of a substrate 137 having a magnetic layer138 formed thereover. Magnetic layer 138 has nonmagnetic regions 140therein which may be formed by diffusing germanium or silicon intonickel, cobalt or alloys thereof which destroys the magnetic momenttherein. Magnetic layer 138 is ferromagnetic. Arrows 143 through 146show a flux path formed around nonmagnetic region 147. As is illustratedin FIG. 7, the flux path is completely contained within the magneticlayer 138 without penetrating into the nonmagnetic region 147. Themagnetic flux around nonmagnetic region 148 is shown by arrows 149through 152. Similarly, the magnetic flux around the nonmagnetic region148 is also completely contained within the magnetic layer 138 withoutpenetrating into the nonmagnetic region 148. Nonmagnetic regions may besub-lithographic in dimension for example presently less than 350 nm.Nonmagnetic region 140 may be produced by bombarding a nickel-cobaltalloy layer having a film of germanium thereover with 100 KV Ge ions.

In operation of magnetic device 136 shown in FIG. 7, electrical currentmay be applied to magnetic layer 138 by way of leads 154 and 155. Whensubstantially no magnetic field H is applied, the magnetic flux pathsaround nonmagnetic region 140 will cause device 136 to be in the highresistance state. When a magnetic field H is applied to magnetic layer138 as shown by arrow 157, the applied magnetic field will cause themagnetization of magnetic layer 138 including magnetic flux paths aroundnonmagnetic region 140 to be aligned parallel with arrow 157. Magneticdevice 136 will be in a low resistance state when the magnetization oflayer 138 is saturated in a common direction such as in the direction ofarrow 157.

Referring to FIG. 8, one method for making a magnetic head will bedescribed. A blanket coating of nickel, iron or cobalt or combinationsthereof are deposited on an insulating substrate. The magnetic stripesare defined by lift-off or subtractive lithography. Electron beam orx-ray lithography will be required to obtain spacing between magneticstripes, of the order of 100 Å. The magnetic stripes are then overcoatedwith a high sputtering yield nonmagnetic metal, for example, copper. Thestructure is then planarized by sputter etching or removing nonmagneticmetal on top of the magnetic stripes. The sputter etching can be donefor example with glancing angle ion beam sputtering.

While it is possible to make the magnetic stripes by lithography, theresulting device would be larger than the minimum lithographic featuresize. Another approach for making magnetic head 10 shown in FIG. 1 is touse structural features which provide magnetic structures of theappropriate size directly as a result of the deposition process. Forexample, as shown in FIG. 8, a vicinal face of a single crystalsubstrate is used as a seed layer. Semiconductors such as Si, Ge or GaAsare suitable substrates for the growth of Fe, Ni or Co and their alloys.The vicinal face 161 may be formed by cutting and polishing a singlecrystal substrate at an angle between 1 to 10° away from a majorcrystallographic plane and then annealing the crystal substrate 162 toproduce atomic scale steps 164 through 167 and surfaces 176-180 formingvicinal face 161. The separation between interplanar steps is determinedby the angle of misalignment of vicinal face 161 from a low Miller indexplane shown by arrow 175. Subsequently, magnetic material 170 isdeposited under conditions of for example a pressure of 10⁻⁸ Torr orless and a substrate temperature of at least 100° C. so it only grows atthe step. In the early stages of growth, the magnetic material 170 growsas isolated particles along the steps 164 through 167. At a later stage,the particles begin to coalesce in a direction parallel to steps 164through 167 but have a greater distance perpendicular or transverse tosteps 164 through 167. Magnetic material 170 may be ferromagneticmaterial, for example, Fe, Co, or Ni or alloys thereof. Substrate 162may be held at ambient temperature or higher. In this way, an array ofparallel magnetic stripes 171 through 174 can be made which is muchsmaller than the minimum lithographic feature size. Magnetic stripes 171through 174 are overcoated with a nonmagnetic metal of comparablethickness such as copper. The upper surface of the nonmagnetic metal isplanarized so that there are alternating regions of magnetic andnonmagnetic metals on the vicinal face 161. Magnetic keepers can bedeposited through masks generated by conventional lithography at the endof magnetic stripes 171 through 174. The magnetic keepers should have alower spontaneous magnetization and/or thickness so that the totalmagnetic flux carried by the magnetic keeper is approximately one halfthe flux carried by the respective magnetic stripes 171 through 174 eventhough the magnetic stripes may have a very different cross sectionalarea.

A magnetic head has been described transverse to the long axis of themagnetic stripe and a means for measuring the electrical resistance ofthe current flowing through the plurality of magnetic stripes upon theapplication of the magnetic field which may be 30 Oe or less to themagnetic stripe.

Further, a method for fabricating a magnetic head has been describedcomprising the steps of orienting, cutting and polishing or selecting asingle crystal substrate having a surface at an angle between 1 and 10°away from a major crystallographic plane, annealing the crystal toproduce atomic scale steps on its surface, depositing a ferromagneticmetal such as Fe, Co, or Ni or alloys thereof onto the single crystalsubstrate surface with the substrate held at ambient temperature orhigher, overcoating the ferromagnetic metal with a nonmagnetic metal ofcomparable thickness and planarizing the nonmagnetic metal to formalternating regions of magnetic and nonmagnetic metals on the surface ofthe substrate.

While there has been described and illustrated a magnetic head forsensing a magnetic field by the giant magnetoresistive effect (GMR), itwould be apparent to those skilled in the art that modifications andvariations are possible without deviating from the broad scope of theinvention which shall be limited solely by the scope of the claimsappended hereto.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent is:
 1. An apparatus for sensing an externalmagnetic field by the giant magnetoresistive effect comprising: asubstrate; a plurality of magnetic stripes fanned over the substrate,each of the plurality of magnetic stripes having a length withrespective ends and a cross-sectional area of less than 1000 Å², theplurality of magnetic stripes being spaced apart side by side over thesubstrate such that stray magnetic fields at the ends of the pluralityof magnetic stripes provide a magnetostatic coupling to the ends ofadjacent magnetic swipes whereby alternating magnetic stripes within theplurality of magnetic stripes are magnetized in alternating directionsat times an external magnetic field is below a first value; anonmagnetic conductive material fanned within a plurality of spacesinterposed between the plurality of magnetic stripes to form aconductive path through the plurality of stripes in series; and meansfor detecting a change in resistance through the plurality of magneticstripes in series as a function of a second value of the externalmagnetic field applied to the plurality of magnetic stripes above thefirst value of the magnetic field, where the second value of themagnetic field aligns the magnetizations of the plurality of magneticsnipes in the same direction.
 2. The apparatus of claim 1 wherein eachof the plurality of magnetic stripes is spaced apart at least 100 Å toprevent exchange coupling.
 3. The apparatus of claim 1 wherein theplurality of magnetic stripes has a respective plurality ofsubstantially parallel longitudinal axes.
 4. The apparatus of claim 1wherein the plurality of magnetic stripes is formed from a soft magneticmaterial.
 5. The apparatus of claim 1 wherein each of the plurality ofmagnetic stripes is substantially the same length and positioned side byside.
 6. The apparatus of claim 5 wherein the ends of the plurality ofmagnetic stripes are magnetically connected by a plurality of transversemagnetic stripes which function as permeable “keepers”.
 7. The apparatusof claim 6 wherein the plurality of transverse magnetic stripes iselectrically insulated from the plurality of magnetic stripes.
 8. Theapparatus of claim 1 wherein the nonmagnetic conductive material is anonmagnetic compound formed from an element of the plurality of magneticstripes.
 9. The apparatus of claim 8 wherein the nonmagnetic compound isformed by diffusing germanium or silicon into nickel, cobalt or alloysthereof.
 10. The apparatus of claim 8 wherein the nonmagnetic compoundis formed by bombarding a nickel-cobalt alloy layer having a film ofgermanium thereover with germanium ions.
 11. The apparatus of claim 1wherein the means detecting includes means for applying electric currentthrough the conductive path.
 12. The apparatus of claim 1 furtherincluding the combination of a magnetic head and a magnetic diskoperating system for storing and retrieving data on a magnetic diskwherein the apparatus is mounted in the magnetic head for retrievingdata.
 13. The apparatus of claim 12 wherein the plurality of magneticstripes is positioned within the magnetic head with a plurality oflongitudinal axes thereof parallel to the magnetic disk.
 14. Theapparatus of claim 12 wherein the plurality of magnetic stripes ispositioned within the magnetic head with a plurality of longitudinalaxes thereof perpendicular to the magnetic disk.
 15. The apparatus ofclaim 1 wherein the cross-sectional area of less than 1000 Å providesthat a plurality of domain walls within the plurality of magneticstripes nucleates thermally.
 16. An apparatus for sensing an externalmagnetic field by the giant magnetoresistive effect comprising: asubstrate; a plurality of magnetic stripes formed over the substrate,each of the plurality of magnetic stripes having a length withrespective ends and a cross-sectional area of less than 1000 Å² suchthat a magnetic response threshold is absent the plurality of magneticstripes being spaced apart side by side over the substrate such thatstray magnetic fields at the ends of the plurality of magnetic stripesprovide a magnetostatic coupling to the ends of adjacent magneticstripes whereby alternating magnetic stripes within the plurality ofmagnetic stripes are magnetized in alternating directions at times anexternal magnetic field is below a first value; a nonmagnetic conductivematerial formed within a plurality of spaces interposed between theplurality of magnetic stripes to form a conductive path through theplurality of stripes in series; and means for detecting a change inresistance trough the plurality of magnetic stripes in series as afunction of a second value of the external magnetic field applied to theplurality of magnetic stripes above the first value of the magneticfield, where the second value of the magnetic field aligns themagnetizations of the plurality of magnetic stripes in the samedirection.
 17. An apparatus for sensing an external magnetic field bythe giant magnetoresistive effect comprising: a substrate; a pluralityof magnetic stripes formed over the substrate, each of the plurality ofmagnetic stripes having a length with respective ends and across-sectional of less than 1000 Å² such that a magnetic responsehysteresis is absent the plurality of magnetic swipes being spaced apartside by side over the substrate such that stray magnetic fields at theends of the plurality of magnetic stripes provide a magnetostaticcoupling to the ends of adjacent magnetic swipes whereby alternatingmagnetic stripes within the plurality of magnetic stripes are magnetizedin alternating directions at times an external magnetic field is below afirst value; a nonmagnetic conductive material farmed within a pluralityof spaces interposed between the plurality of magnetic stripes to form aconductive path through the plurality of stripes in series; and meansfor detecting a change in resistance through the plurality of magneticstripes in series as a function of a second value of the externalmagnetic field applied to the plurality of magnetic stripes above thefirst value of the magnetic field, where the second value of themagnetic field aligns the magnetizations of the plurality of magneticstripes in the same direction.